High-low impedance electron tube detector



Filed Nov. 29, 1945 Jan. 25, 1949. I H. H. WITTENBERG 2,460,160

HIGH-LOW IMPEDENCE ELECTRON TUBE DETECTOR 2 Sheets-Sheet 2 I r z c/fiewrak I Z c I rm anew) INVENTOR ATTORNEY Patented Jan. 25, 1949 UNITEDSTAT HIGH-LOW IMPEDANCE ELECTRON TUBE DETECTOR Hubert H. Wittenberg,Lancaster, Pa., assignor to Radio Corporation of America, a corporationof Delaware Application November 29, 1945, Serial No. 631,723

6 Claims. (Cl. 250-27) This invention relates to protective systems suchas are useful in producing an effect in response either to a relativelylow impedance or to a relatively high impedance between a pair ofconductors which may be, for example, the two rails of a railwaycrossover or the like.

It is well known that there exists between the rails of any section of arailway an impedance which varies with the weather from a relatively lowimpedance in Wet weather to a, relatively high impedance in dry weather.Such variation in impedance is denoted herein as the normal range ofvariation in the impedance between the two rails or conductors. Anyprotective system associated with such conductors must of course beinsensitive to this normal range of values of the impedance between theconductors.

The protective system, however, should be sensitive to impedances outsidthe normal range. Thus in the case of a short circuitbetween the twoconductors when the impedance is below the normal range, the protectivesystem should produce an effect such as lighting a red signal. Likewisein the case of an open circuit when the impedance is above the normalrange, the system should produce the same effect.

In accordance with the present invention, this result is achieved by'aprotective system wherein (l) a unilateral impedance device such as 2.rectifier is connected between the conductors'at one of their ends, (2)an alternating potential input means and a resistor are connected inseries between the conductors at the other of their ends, (3) a pair ofelectron discharge devices connected in push-pull relationship eachhaving applied to its anode and shield grid alternating potentials whichare arranged to be of opposite polarity for ensuring its deenergizationwhen the potential of its control grid decreases to a predeterminedposi-' tive value, and (4) alternating potential bias means areconnected between the conductors and the controlgrid circuits of the twoelectron discharge devices so that one of the devices is deencrgizedduring the positive halt cycle of its anode potential in response to an.impedance lower than the normal range and the other of said devices isdeenergized during the negative half cycle of its anode potential inresponse to an impedance higher than the normal range.

An important feature of one modification of the invention is theinterconnection of the oathode heater and the shield grid of each deviceso that the device is d'eenergiz'ed in response to fail-' ure of theshield grid circuit.

Important objects of the invention are the provision of an improvedprotective system which is insensitive to a predetermined or normalrange of impedance values but is sensitive to impedance values above orbelow such range, the provision of a protective system which alwaysfails safef so that any defect in the system instantly produces a dangersignal, and the provision of an improved protective system and method ofoperation whereby failure of the system or dangerous conditions of thecircuit protected are immediately indicated by a danger signal. r Theinvention will be better understood from the following descriptionconsidered in connection with the accompanyingdrawings and its scope isindicated by the appended claims.

Referring to the drawings: Figure 1 is a wiring diagram of onemodification of the invention, 7 Figures 2A to 2B are explanatory curvesrelating to the operation of the system of Figure 1, and Figure 3 is awiring diagram of a modified form of the invention. v

The system of Figure 1 includes a pair of con ductors Ill and II.Connected between these conductors at one of their ends is a unilateralimped-' ance device l2 illustrated as a copper oxide rectifier. At theother of their ends the two conductors are interconnected through aresistor l3 and alternating potential input means I4 illus trated as thesecondary winding of a transformer. Dotted line resistors R1 and R2 areintended to denote the normal range of variation in the impedancebetween the conductors.

A pair of electron discharge devices l5 and IE connected in push-pullrelationship have potential applied to their anodes and shield gridsfrom the secondary windings Ts! to T85 of a transformer I I. It shouldbe observed that (1) current also is supplied from the secondary Ts3 tothe cathodeheaters of the devices I5 and I6, (2) a relay RL! shunted byan 8 microfarad capacitor is connected in the anode circuit of thedevice l5, and (3) a relay RLZ shunted by an 8 microfarad capacitor isconnected in the anode circuit of the device I6. I

These relays RM and RL2 are series-connected in a control circuit in awell known manner so that deenergization of either of them actuates acontrolled device such as a danger signal.

Bias potential for the control grids of the devices l5 and i5 is appliedthrough a transformer winding T35 and a pair of 500 ohm resistors l8 andi9. Control potential is applied to" the con, trol grids from a 10k.-resistor 20 which is connected between the conductors l0 and H at the"near end of the conductors. The control grid circuit of the device [5is from the cathode through the resistor 20, the resistor I8 and a 100k. resistor 2| (shunted by 0.1 microfarad capacitor) to the controlgrid. The control grid circuit of the device is from the cathode throughresistors 20, i9 and 22 to the control grid. Eachof these control gridcircuits is shuntedby a separate 0.002 microfarad capacitor,

Figures 2A to 215 show the relation between;

the various alternating potentials involved in the operation of thesystem. c

In Figure 2A, the critical voltage below which the device I5 isdeenergized. is denoted by a dotted line curve and the anode and shieldgrid voltages of the device 15 are denoted respectively by the curves[es and leccz.

In Figure 2B, the bias voltage applied through as that of Figure 1 withthe exception that failure of a shield grid circuit of Figure 3deenergizes the defective device.

In the modification of Figure l, a danger signal is produced byinterruption of the alternating potential supply; failure of theelectron emission of either of the devices IE or IS, a break in any ofthe control grid resistors which permits the shield grid to deenergizethe device, and failure the transformer secondary to the control grid. I

of the device I5 is indicated by the curve lecci.

In Figure 2C, the curveea denotes the potential applied by the secondarywinding M, the curveet denotes the potential actually applied betweenthe conductors when current flows through the normal impedance betweenthe conductors, the curve leer (no train) denotes the resultantpotential applied to the control grid of the device [5 when theimpedance between the conductors is within its normal range and thecurve leg (with train) denotes the potential applied to the control gridof the device l5 when the impedance between the conductors is below itsnormal range.

It will be noted that. in passing from the potential [e01 (no train) tothe potential lecl (with train), the control grid of the device i5assumes the critical grid voltage of this device.v This results indeenergization of the device I 5 and operation of the relay RLi aspreviously explained.

In Figures 2D to 2F, the various potentials involved in the operation ofthe tube 28 are shown. In these figures, 26b denotes anode voltage, 2cmdenotes shield grid voltage, 2cm denotes control grid bias voltage, 2c1(track 07c) denotes the resultant control grid voltage when theimpedance between the conductors is within its normal range and Zen(track open) denotes the resultant control'grid voltage when theimpedance between the conductors is above its normal range.

It will be noted that in passing between the potentials 2601 (track ck)and 2601 (track open) the control grid of thedevice l6 assumes thecritical grid voltage of this device. This results indeenergization ofthe device I 6 and operation of the relay RL2 as previously explained.

The electron discharge devices I5 and I 6 of Figure 1 are gaseouselectron discharge devices of the RCA 2050 type. In their stead may .beused gaseous electron discharge devices of the RCA 2D21 type which areprovided with exe ternal leads to the opposite ends of their shieldgrids.

Figure 3 shows how the RCA 21321 device is connected into the circuit.Thus. the cathode heaters of the devices i5 and i 5' are connected inseries with their shield grids to the transformer secondaries E93 and Tsl, and the cathodes of the two devices are-connected to the adjustablecontacts 24 and 25 of resistors 25 and 27 whichare connectedrespectively across the secondary T53 and. the secondary Tsd. With theseconnections, any break of the shield grid circuit deenergizes the deviceso that the. system. fails safe-(with a red light showing) v V VFigure3also shows a 1 k. resistor in serieswith of the rectifier whichdeenergizes the device l6. The modification of Fig. 3 affords the addedprotection that a danger signal is produced by interruption of theshield grid circuit which terminates electron emission and deenergizesthe device.

. Important advantages of the present invention are that it'isinsensitive to impedance changes within a normal range but is sensitiveto impedance without such range and that it produces a danger signal (1)in response to any interconductor impedance without the normal range and(2) in response to failure of the protective system itself.

, I claim as my invention:

The combination of a pair of electron discharge devices connected inpush-pull relation and each having a cathode, an anode and con trol andshield grids, means for applying alternating potentials of oppositepolarities to the anode. and shield grid of each of said devices, a

40 pair of conductors, and means interconnecting said. conductors witheach other and with said control grids for deenergizing one of saiddevices when the impedance between said conductors assumes apredetermined relatively low value and for deenergizing the other ofsaid devices when said impedance assumes a relatively high value.

2. The combination ofv a pair of electron dischargedevices connected inpush-pull relation and each havin a cathode, cathode-heater, an anodeand control and shield grids, means for applying through the cathodeheater to the shield grid of each of said devices an alternatingpotentialof a polarity opposite to that of its anode, a pair ofconductors, and means interconnecting said conductors with one anotherand with said control grids for. deenergizing one of said devices when:the impedance between said conductors assumes a relatively low value andfor deenergizlng the other of said devices when said impedance assumes arelatively high value.

3; The combination of a pair of electron discharge devices connected inpush-pull relation and each having a cathode, an anode and control andshield grids, means for applying alternating potentials of oppositepolarities to the anode and shield grid of each of said devices, a pairof con duct'or's, a rectifier connected between said corductors at oneof their ends, a resistor and alter-- hating potential input meansconnected in series between said conductors at the other of their ends,and means interconnecting said conductors andsaid control gridsiordeenergizing one of said devices when the impedance between said.conductors assumes-a relatively lowvalue and for 4. The combination of apair of electron discharge devices connected in push-pull relation andeach having a cathode, an anode and control and shield grids, means forapplying alternating potentials of opposite polarities to the anode andshield rid of each of said devices, and means interconnecting saidconductors with one another and with said control grids for deenergizingone of said devices during a positive half cycle of its anode potentialin response to a relatively low irnpedance between said conductors andfor deenergizing the other of said devices during a negative half cycleof its anode potential in response to a relatively high impedancebetween said conductors.

5. The combination of a pair of electron discharge devices connected inpush-pull relation and each having a cathode, an anode and control andshield grids, means for applying alternating potentials of oppositepolarities to the anode and shield grid of each of said devices, andmeans interconnecting said conductors with one another and with saidcontrol grids for deenergizing one of said devices during a positivehalf cycle of its anode potential in response to a relatively lowimpedance between said conductors and for deenergizing the other of saiddevices during a negative half cycle of its anode potential in responseto a relatively high impedance between said conductors, and relay meansfor producing an effect in response to deenergization of either of saidde- V1088.

6. The combination of a pair of electron discharge devices connected inpush-pull relation and each having a cathode, an anode and control andshield grids, means for applying alternating potentials of oppositepolarities to the anode and shield grid of each of said devices, a pairof conductors, a rectifier connected between said conductors at one oftheir ends, a resistor and alternating potential input means connectedin series between said conductor at the other of their ends, meansconnecting one of said conductors to the cathodes of said devices, andalternating potential bias means connected between the other of saidconductors and said control grids.

HUBERT H. WITTENBERG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Boerner et a1 Dec. 10,

